Vehicle manufacturers have realized that it may be desirable under some conditions to automatically start and stop an engine of a vehicle. Stopping the engine can reduce fuel consumption, especially when the vehicle is stopped for longer periods of time, in stop-and-go traffic for example. In some start/stop systems the transmission may be tied-up by actuating one or more transmission clutches during the engine stop. By tying up the transmission it is possible to reduce driveling wind-up. However, once the transmission is tied-up it has to be released from tie-up such that disturbances to the driver are reduced. If the transmission is released to early the driver may notice vehicle movement that may not be expected. On the other hand, if the transmission is released late, the vehicle may not launch as the driver desires.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for improving engine starting and vehicle launch for a vehicle with an automatically stopped engine.
One embodiment of the present description includes a method for starting an engine coupled to a transmission, comprising: stopping said engine; applying a tie-up force to said transmission during said engine stop; and reducing said tie-up force in response to an amount of torque transmitted to said transmission via a torque converter and an amount of force applied by a vehicle brake.
By reducing transmission tie-up force in response to torque transmitted to a transmission an amount of vehicle brake force, it is possible to launch the vehicle in response to driver's input such that the vehicle launch may be less objectionable to the driver. For example, if the transmission tie-up force is low and the amount of vehicle brake force is high, the transmission tie-up force can be reduced at a rate that is higher than if the transmission tie-up force is set high in response to low vehicle braking force.
The present description may provide several advantages. Specifically, the approach may improve vehicle launch for engines that are automatically stopped. Further, the method may reduce transmission clutch wear since transmission tie-up release can be adjusted for vehicle launch conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.